Method for producing high density sintered products



A. w. HULL Oct. 13, 1942.

Filed y 29, 1941 ventor: W. l'lul l,

' v In Albe b 9 His Attorne METHOD FOR PRODUCING HIGH DENSITY SIN'EEBED PRODUCTS Albert W. Hull, Schenectady, N. IL, assignor to General Electric Company, a corporation of "ewlfo'rk Application May 29, 1941, Serial No. 395,793 7 Claims. (Cl. 75-22) The present invention relates to pressed powwhich will not warp when sintered. Other obdered materials and more particularly to a jects will appear hereinafter. method for producing high density pressed and The novel features which are characteristic sintered products. Prior to the present invenof my invention are set forth with particularity tion, the process generally employed in the fabri- 5 in the appended claims. My invention, however, cation of pressed powdered materials comprised will best be understood by reference to the folthe materialsto be pressed in a steel mold and lowing specification when considered in connecapplying pressure directly to the powdered intion with the accompanyin r w n in wh ch gredients by means of a plunger. Fig. 1 is a view partly in section, partly in ele- In pressing powdered materials it always is vation, of an apparatus whereby my e t n desirable to obtain a product which has a unimay be carried into eifect; 2 is a Similar V form maximum density throughout its mass. A illustrating the position of the various portions maximum density in an alloy can be approached of the mold when the Pow edients by employing a pressure considerably higher than he e h ve been compr ss d; F g. 3 is a perthe maximum flow strength of at l a t one of spective view of the various portions of the mold the components of the alloy in its work hardemployed in ca ry n out my e o whi e ened condition. Generally, however, in the pro- Fig. 4 is a perspective view of 'a super rg r turduction of pressed powdered materials which are in bucket made in accordance with y thereafter sintered, lower pressures than that are Proved P employed so that although some flow takes place Referring more particularly to the drawing, I the flow stops before all the crevices are filled a have indicated at I a Steel mold which comprises result which is due to distortion of the powdered stationary po 2 and 3 and a o b p un particles and the tendency to make them fit toer element e parts 2 a 3 a p s t oned gether which at the same time work-hardens in P p alignment y means of dowel P them. In one method of carrying out my invention, By employing a pressure of about 003 the powdered ingredients 6 are impregnated with pounds per square inch, which is well above the Paramn in solution, mixed thoroughly, n dr d flow point of some of the pure metals for and placed in the mold l. The powdered mateample electrolytic iron, it is possible to obtain rial preferably has fineness capable of Passing uniform maximum density of the metal could be a pressed powdered iron product having a thmltgh 200 to 400 ntesh screw The density of 7.70 which is within 2% of the maxi- Perm! the PWdered mgredients P easfly mum density of iron. Under these conditions, under The powdered ingredlents are if it were possible to obtain a uniform distribupreformed m the mold under a pressure of tion of the powdered material over the cross secabout 300300 pounds per square inch 5 then tion of the mold, it might be expected that a at a temperature m a reducing atmosphere such as pure dry hydrogen. A temperature of about 500 C. is high enough obtained by ordinary compression means. I have to distill the paraflin and deoxidize the pressed found, however, that if the distribution of the powder material but is not high enough to cause powdered material is non-uniform so that one c mom mm is.. it: asse ts another portion then the force necessary to 1' ed cause the compressed powder to flow from t in i fl ie m l l z ii i e xi l t a pz gr tfiig hra gm l full end to the shallow end of the mold may be is placed on top of the pressed material and a greater than the component of pressure avail- 5 ressure of about 300 000 Ounds a He able to cause this flow. Under such conditions gleam of a plunger 4. The reafter tlfia pr ss c l the plunger will be stopped after completely commaterial may smtered, for example by heat pressing the fun end of the and the shaling for several ours at an elevated temperature low end will-be incompletely oompressedbut below the melting point of the alloy. If"

It is one of the-objects of the present invento d ired, the rubber or other flexible pad emt t p v d a m h d for p s-8 p w ployed may be secured to the base of the plunger,

materials which will result in a product of unior may be placed below the powder; or pads may form density throughout the mass of the pressed be placed both below and above the powder, or

material. A further object of the invention is the powder may be surrounded completely by the production of a pressed powder product rubber or the like.

If the powdered materials are pressed without the use of a flexible pad, soft spots will occur wherever there is a scarcity of powder. Such spots are present even when paraflin has been used in preforming the powder material. Be.- fore sintering, these reveal themselves by softness and mechanical weakness; after sintering by excessive shrinkage, causing deformation of shape, and by weakness. These defects are absent when a flexible pad is employed, but the contour will be irregular to the extent of the local scarcity of powder. However, if the material is preformed as hereinbefore set forth, this irregularity will be minimized.

The present process is particularly adapted for the production of complex shapes, for example supercharger turbine buckets. A bucket 8 of that type, as indicated in Fig. 4 of the drawing, is crescent shaped in cross section being relatively thick at its deepest portion and tapering therefrom to relatively thin edge portions. Such devices, when produced in accordance with my improved process, remain straight when sintered. However, it produced without the use of a flexible pad the pressed material will curl in the direction of its length.

The flexible pad should be thick enough to permit equalizing the pressure on the powdered ingredients and in general a thickness of about v to of an inch will provide satisfactory results.

If desired, the flexible pad may be employed in the 'prei'orming operation but preferably it is employed in the final pressing operation after the material has been preformed. without the pad. Both methods, however, will yield straight, undistorted products such as turbine buckets and the like.

The preforming may be omitted when articles of regular shape, such as rectangular bars, are to be made. In this case no paraffin is used. The powder material, after mixing, is distributed as evenly as possible in the mold, pressed directly to final form and uniform density with the aid of the rubber pad, and sintered. Or the pressing operation may be performed in two steps, first without the rubber pad and then with it.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. The method for fabricating a body of complex shape and uniform density from powdered ingredients which comprises placing the powder and through a flexible to-be pressed in a rigid mold which has the irregular contour of one of the surfaces of said body, applying pressure to said powder by a rigid plunger and flexible pad, said pad being positioned between the plunger and the body to be pressed and the surface of said plunger having an irregular contour substantially identical with the opposite surface of said body.

2. The method for preventing distortion in a sintered product made from powdered ingredients which comprises preforming the powdered materials into a desired irregular shape, heating the preformed material in a reducing atmos phere at a temperature sufliciently high to deoxidize the material but insufficient to cause shrinking or sintering, thereafter applying pressure to the preformed material in a rigid mold material.

3. The process of fabricating a pressed powder body which comprises mixing powdered materials comprising said body with paraflin or the like, drying the mixture, pressing it into a desired shape, heating the mixture in a reducing atmosphere at a temperature sumciently high to drive out the paraflin an deoxidize the shaped material but not to cause sintering or shrinkage, placing the shaped material in a mold and applying pressure to it through flexible means in direct contact with said shaped material.

4. The method for producing a turbine bucket from powdered material which comprises placing mixed ingredients comprising said powder "in a mold having the contour of one of the surfaces of said bucket, applying pressure thereto by a plunger and flexible pad, said pad being in direct contact with said ingredients, said plunger havbig a contour substantially identical with the opposite surface of said bucket.

5. The method of making a turbine bucket which comprises preforming powdered ingredients comprising said powder into substantially the shape of said bucket, placing said preformed bucket in a mold having a contour substantially identical with one side of said bucket, covering said bucket with a flexible pad and applying pressure to it through said pad by means of a plunger having a contour substantially identical with the opposite side of said bucket and thereafter sintering said bucket.

ALBERT W. HULL.

pad in contact with said 

